The Penicillins

V. ABSORPTION, DISPOSITION, AND METABOLISM
TABLE 16. PHARMACOKINETIC PROPERTIES OF THE PENICILLINS
Penicillin
(Dose)
% Oral
Absorp.
Food Ø
Absorp.
%
Protein
bound
40
%
Metab.
Total
Conc.
(µg/ml)
Free
Conc.
(µg/ml)
t1/2
(hrs)
normal
Pen G 30 Yes 55 20 2 0.9 0.5 10
Pen V 60 No 80 55 4 0.8 1.0 4
t1/2
(hrs)
renal
imp
Methicillin Nil 35 10 0.5 4
Oxacillin (0.5 g po) 30 Yes 93 45 6 0.4 0.5 1
Cloxacillin (0.5 g po) 50 Yes 94 20 10 0.6 0.5 1
Dicloxacillin(0.5 g po) 50 Yes 97 10 15 0.45 0.5 1.5
Nafcillin (1g) Erratic Yes 87 1.2 0.16 0.5 1.5
Ampicillin (0.5g po) 40 Yes 17 10 3.5 2.9 0.5 1.5
Amoxicillin (0.5g po) 75 No 17 10 7.5 6.2 1 8
Bacampicillin (0.8g) 95 No 17 10 12.9 10.7 0.5 1
Carbenicillin
indanyl
30 No 50 2 15 7.5 1.1 15
Ticarcillin (3 g) Nil 50 15 190 85 1.2 15
Piperacillin (2g IV) Nil 30 300 150 1.3 4
Clavulanic
acid (0.125 g po) 90 No 25 55-75 3.3
Sulbactam (0.5g IV) Some 38 10 13 7.8 1 4
Tazobactam Nil
Temocillin Nil 85 10 4 17
Adapted from Mandell, Douglas, & Bennett, Principles and Practice of Infectious Diseases, 3rd ed.,
Churchill Livingstone, New York, 1990.
1. All penicillins have short half-lives (0.5-2 h) and must be given 3-4 times per day.
2. Penetration into CSF - very low when meninges are not inflamed. Penicillins with highest
CSF penetration are ampicillin (mean 35% of serum, range 2-100%), ticarcillin (mean =
9.5% and 40% in 2 different studies), and piperacillin - (mean = 23% and 32% in 2
studies). Penicillinase-resistant penicillins (methicillin & nafcillin) show very poor
penetration.